NVMe: Don't unmap controller registers on reset

NVMe: Don't unmap controller registers on reset

Unmapping the registers on reset or shutdown is not necessary. Keeping
the mapping simplifies reset handling.

Signed-off-by: Keith Busch <keith.busch@intel.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit b00a726a9fd82ddd4c10344e46f0d371e1674303)

Orabug: 24758839
Conflicts:
The changes are merged manually as the nvme upstream is not in sync with
UEK4 QU2
    drivers/nvme/host/pci.c

Signed-off-by: Ashok Vairavan <ashok.vairavan@oracle.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Dhaval Giani <dhaval.giani@oracle.com>